A continuously variable transmission (CVT), that contrasts with other mechanical transmissions that only allow a few different distinct gear ratios to be selected, is a transmission capable of change steplessly through an infinite number of effective gear ratios between maximum and minimum values. As CVT is capable of allowing the the engine speed to remain at its level of peak efficiency with improved fuel economy and exhaust emissions, it is becoming the transmission of choice for all kinds of modern and future vehicles. There are a variety of CVTs being developed by different manufacturers, among which the metal V-belt CVT and the toroidal CVT are the most common types of CVT. In the metal V-belt stepless CVT, there are two parallel-disposed pulleys that are split perpendicular to their axes of rotation, with a V-belt running between them. As the two pulleys are connected respectively to an input shaft and an output shaft, the input shaft and the output shaft are required to be disposed parallel to each other so that the space needed for accommodating such metal V-belt stepless CVT is comparatively larger, not to mention that the metal V-belt stepless CVT will require a large hydraulic system for power transmission control and speed ratio adjustment. On the other hand, the toroidal CVTs are made up of two traction discs and two rollers, in which the discs, being formed as two almost conical parts disposed coaxially and point to point, are connected respectively to the input and the output shafts, and the rollers are disposed for allowing the same to move along the axis of the near-conical parts, changing angle as needed to maintain contact so as to transfer power from the input disc to the output disc by the friction of the contact. As the input shaft and the outshaft in the toroidal CVTs are coaxially disposed, it requires less space for accommodating the same. In addition, comparing with the metal V-belt CVTs, speed ratio adjustment in the toroidal CVTs can be performed with less power. Nevertheless, both the metal V-belt CVT and the toroidal CVT have their pros and cons, considering different applications.
According to the shape of the rollers housed between the two toroidal-shaped discs, the toroidal CVTs can be divided into three types, which are ball toroidal CVTs, half-ball toroidal CVTs and wheel toroidal CVTs. Among which, since the ball toroidal CVT is able to provide a comparatively more stable power transmission and it can change the rotation speed ratio of the input and the output shafts simply by tilting the rotation spindles of the its two friction balls for allowing the two to contact the discs at different areas, the ball toroidal CVT is regarded as the most promising CVT for future applications. There are already many studies relating the improvement of the ball toroidal CVT, such as those developed by Fallbrook Technologies Inc. U.S.A and disclosed in U.S. Pat. No. 2,469,653 and U.S. Pat. No. 5,236,403. The ball toroidal CVTs disclosed in the patents of the Fallbrook Technologies Inc. are characterized in that: the speed adjusting can be achieved by enabling a friction ball carrier on which the friction balls with their ball spindles are mounted to move parallel along the hub axis of the CVT as the tilting angles of the friction balls are changed thereby.
Although the aforesaid ball toroidal CVTs have the following advantages: it requires less parts for configuring the same and the there is less resistance being caused during speed adjusting, it is still not feasible for any practical usage since there are difficulties for applying the ball toroidal CVT in automatic electric speed control. Therefore, the ball toroidal CVTs are currently being used as the transmissions for bicycles. Moreover, with the advance of artificial intelligence (AI), it is in need of an improved CVT capable of using an evaluation of an embedded AI algorithm to control an electric motor for driving its speed adjusting mechanism to act accordingly and thus achieving an optimal output.